In a multitude of the thermal processes the process equipment is heated up by a preheat burner installation before the start of the main burner system needed for the continuous and designated plant operation. When the main burner system is operated, the preheat burner is shut down. All modes of burner operation are regulated by national or international regulations such as the EN-746-2 or equivalent. To avoid hazardous operation resulting from incomplete combustion, the violation of the parameters stipulated in such regulations, which define a permissible or hereinafter called critical operating range, results in mandatory shut downs of the burner system. The currently used modes of operation and processes result in an enforced shut down of the burner system and subsequently the entire process if the safety relevant parameters, in particular temperature, air/fuel ratio, O2-concentration etc. in the reactor, are violated. In addition, the reactor often has to be purged resulting in a significant loss of temperature, time, heating fuel and production since reheating for a restart of the reactor is required.